Disk drives are information storage devices that use rotatable disks with concentric data tracks containing the information, read/write heads or transducers for reading and/or writing data onto the various tracks of the disks, and a rotary actuator connected to carriers for the heads for moving the heads to the desired tracks and maintaining them over the track centerlines during read or write operations. The rotary actuator is a voice coil motor (VCM) comprising a coil movable through a magnetic field generated by a fixed permanent magnet assembly. The current to the coil of the VCM actuator is controlled by a servo control system that uses head-positioning information read from the disks. There are typically a plurality of disks separated by spacer rings and stacked on a hub that is rotated by a disk drive motor, also called a spindle motor. A housing supports the spindle motor and actuator, and surrounds the head and disks to provide a substantially sealed environment for the head-disk interfaces.
In conventional magnetic recording disk drives, the head carrier is an air-bearing slider that rides on a bearing of air above the disk surface when the disk is rotating at its operational speed. The slider is maintained next to the disk surface by a suspension that connects the slider to the actuator. The slider is either biased toward the disk surface by a small spring force from the suspension, or is "self-loaded" to the disk surface by means of a "negative-pressure" air-bearing surface on the slider. In contrast to conventional air-bearing disk drives, contact or near-contact disk drives have been proposed that place the head carrier in constant or occasional contact with the disk or a liquid film on the disk during read and write operations.
One of the problems in rotary actuator disk drives is actuator vibration, typically caused by rapid motion of the actuator and air flow from the rapidly spinning disks. Actuator vibration causes instability in the servo control system and track misregistration, which limit the track density that can be achieved. The most troublesome vibration modes are the "butterfly" mode, wherein the coil and the actuator arm are stressed about the actuator pivot toward each other, and the arm modes, wherein the actuator arms sway in plane with different amplitudes and directions. All these modes involve relatively large sway motion of the actuator arm.
What is needed is a rotary actuator that has minimal vibration, especially at the butterfly mode and the arm modes, so that high track density can be achieved.